This invention relates generally to a heat exchange system for personal use to provide beneficial cooling or warming effects, depending on the operating mode of the system, and more particularly to a system which includes replaceable thermal cartridges insertable in a fabric holder adapted to engage and conform to the skin of the user.
The interior of the human body has a normal temperature level which is usually said to be 98.6.degree. F. But actually, in the course of each 24-hour period, the body temperature goes above and below this nominal value within a 1.8.degree. F. range. Body temperature is determined by the relationship existing between the amount of heat internally generated, which depends on basal metabolism, and the amount of heat escaping from the body. Additional heat is produced as a result of muscular activity, this being dissipated by an increase in radiation, conduction or evaporation from the skin surface and by more rapid and deep breathing. Thus the skin is the interface between the internally heated body and the atmosphere, and is in heat exchange relationship therewith. If the heat produced by a body surpasses heat losses therefrom, this gives rise to fever; but if heat losses exceed heat production, then the body temperature falls below the nominal value, resulting in shivering and hypothermia.
The nerve centers for regulating body temperature are located in the forebrain region called the hypothalamus. When these nerve centers sense a decrease in blood temperature, they stimulate skeletal muscles to increase activity and they also stimulate the liver to enhance the expenditure of energy, thereby contributing heat to the blood. An increase in blood temperature causes the hypothalamus to call for the secretion of sweat and to route more blood to the skin areas, glandular activity of the liver then being inhibited and the general tonus of the skeletal muscles being lowered. These changes reduce body heat production and increase heat losses.
One can, to a limited degree, accommodate the body to widely different environmental conditions by appropriate clothing. Thus clothing providing good thermal insulation makes it possible for an individual to function effectively in severe cold. By wearing light, well-ventilated clothing, one can be reasonably comfortable in a hot climate.
Clothing, therefore, serves as a heat exchange function; for it determines the propagation rate of heat from the body to the atmosphere. When the ambient temperature is well below the body temperature, clothing acts as a thermal insulation to slow down the heat exchange rate and thereby reduce the loss of heat; and when the ambient temperature is well above body temperature, the rate at which heat is lost from the body is enhanced by suitable clothing, particularly if it acts as a wick to disperse sweat over a broad area to promote evaporative cooling.
There are, however, many situations where regardless of the clothing worn, the clothing is incapable of maintaining the body temperature at an acceptable level. Thus athletes, such as long-distance runners, tennis players and bicycle riders who exercise vigorously in warm environments may be subject to heat prostration, for they are unable to dissipate sufficient heat to maintain a safe body temperature. Even in a relatively cool indoor environment the athlete may sweat excessively, this giving rise to premature fatigue.
On the other hand, when an athlete exercises in a severely cold environment, the resultant increase in heat production may still be inadequate to overcome the rapid transfer of heat from the body to the atmosphere, particularly when the nature of the activity is such that the athlete cannot be heavily bundled in warm clothing.
Attempts have heretofore been made to couple a heat source or heat sink to the body in order to provide a cooling or warming effect. Thus the 1955 patent to Giardini, U.S. Pat. No. 2,715,315, discloses a wrist band which incorporates a dry ice pellet. Since the blood vessels are close to the surface of the wrist area, the device, according to Giardini, has a cooling effect on the entire body. The Amador U.S. Pat. No. 3,149,943 also shows a wrist band applicator, use being made of granular ammonium nitrate which is reacted with water to produce a cooling action. Henderson, U.S. Pat. No. 4,204,543, discloses a coolant band that encircles the head, use being made for this purpose of a freezable liquid. Merna, U.S. Pat. No. 3,465,120, shows a wrist applicator with an electrically-operated heating element.
While the devices disclosed in the above-identified patents seek to supply heat or cold to the body, they are relatively inefficient, for they fail to take into account certain physiological factors and they afford only a short-term cooling or heating action. For example, a battery-operated heater has an effective life that depends on the capacity of the battery. Since the capacity of a battery is related to its size and weight, a battery sufficiently compact to be carried on the person would necessarily have a small capacity.
Though some of these references make use of a gel which can be cooled to provide a heat sink, because this gel draws heat from the body, unless a large mass thereof is employed and the rate of heat transfer controlled, the cooling action of the gel is short lived.